Catalytic Enantioselective Conjugate Addition of Stereodefined Di‐ and Trisubstituted Alkenylaluminum Compounds to Acyclic Enones

Abstract

Catalytic enantioselective conjugate addition (ECA) reactions with readily accessible and stereochemically defined E-, Z-, di-and trisubstituted alkenyl aluminum compounds are disclosed. Transformations are promoted by various NHCcopper catalysts (NHC = N-heterocyclic carbene), which are derived from enantiomerically pure sulfonate imidazolinium salts. The desired products were obtained in up to 89% yield and > 99:1 e.r.; the alkenyl moiety was transferred with complete retention of its stereochemical identity in all instances. The scope and limitations of the approach, key mechanistic attributes, and representative functionalization are presented as well.

Stereoselective Formal Hydroamidation of Si-Substituted Arylacetylenes with DIBAL-H and Isocyanates: Synthesis of (E)- and (Z)-α-Silyl-α,β-unsaturated Amides

“…We began our investigation by examining the reactivity of phenyl isocyanate ( 3a ) toward Si-substituted vinylaluminum reagents, which were generated from the regio- and stereoselective hydroaluminations of Si-substituted phenylacetylenes 1 and 2a with DIBAL-H under the conditions described previously by Hoveyda and co-workers, the results of which are summarized in Table . The addition of phenyl isocyanate to the ( Z )-vinylaluminum directly derived from the reaction of dimethylsilyl-substituted phenylacetylene 1 with DIBAL-H in a mixture of hexanes/THF (5/1) provided only a trace of the desired amide product (entry 1).…”

“…Despite the observed regioselective control and their broad applicability, to the best of our knowledge, no examples of E - or Z -controllable hydroamidation reactions of alkynes have been reported. Hoveyda and co-workers demonstrated several examples of enantioselective carbon–carbon bond forming reactions using E - or Z -pure alkenylaluminum reagents generated in situ from the solvent-controlled hydroalumination of a Si-substituted acetylene with diisobutylaluminum hydride (DIBAL-H) (Scheme g) . Inspired by these studies, we assumed that treating E- or Z -pure Si-substituted alkenylaluminums with isocyanates would lead to the construction of the corresponding E - or Z -α-silyl-α,β-unsaturated amides with high stereospecificities.…”

Development of Earth-Abundant Metals-Catalyzed Enantioselective Alkenylations Using Alkenyl Metal Reagents

“…随后与 NaO t Bu 作用得 到 26, 再异构得到加成产物, 同时再生催化剂, 进入下 一个循环(图 28). 2020 年, Hoveyda 课题组 [38] 报道了 NHC-Cu 催化的 一系列 E-、Z-、二取代以及三取代的烯基铝试剂(由相…”

Sulfonate N‐Heterocyclic Carbene–Copper Complexes: Uniquely Effective Catalysts for Enantioselective Synthesis of C−C, C−B, C−H, and C−Si Bonds

“…Asulfonate NHC-Cu complex may be used for ECAo fa na lkenyl-Al species to an acyclic enone (Schemes 47 and 53). [105] One entails reactions with silyl-substituted alkenyl-Al compounds (Scheme 47 a), formed by regioselective addition of dibal-H to an alkyne.T ransformations with Me 2 HSi-substituted variants are generally higher yielding (vs.Me 3 Si-substituted, which afforded up to 30 % iBu addition byproducts). Efficiencyhinges on electronic attributes of the electrophilic partner,which also influences the identity of the most effective catalyst.…”

“…A sulfonate NHC‐Cu complex may be used for ECA of an alkenyl‐Al species to an acyclic enone (Schemes 47 and 53) [105] . One entails reactions with silyl‐substituted alkenyl‐Al compounds (Scheme 47 a), formed by regioselective addition of dibal‐H to an alkyne.…”